[Aging of hair and nails].

Human hair and nails, like all other organs, undergo chronological aging. Age-associated changes in growth, color, and structure of the hair and nails are common. In contrast to the aging process of the skin, the gerontobiological course of hair and nails has not been investigated comprehensively. Investigations on signaling pathways important for melanogenesis of the hair follicle improve our understanding of processes involved in hair greying. Differences in the structure and quality of the nails at an advanced age are determined mainly by age-dependent variations in lipid content of the nail plates. However, it is important to recognize age-dependent processes in hair shafts and nails and to distinguish between chronological aging and pathological changes. The possibilities to improve these aging processes have, primarily, to be seen in the field of external cosmetic procedures. Since the effect of preexisting hormonal substitution treatment has not yet been adequately investigated, it can be regarded as critical to evaluate the confirmed benefits and possible risks of such treatment either for hair or for nail quality improvement.